To provide an underground heat exchanger burying structure for achieving ground heat utilization low in the installation cost of a ground heat exchanger and excelling in heat exchange effectiveness.

A foam resin board 3 is laid abutting on the bottom face of a mat foundation 2 generally executed as a foundation structure of a building, or abutting on the bottom face of a foundation slab in a pile foundation, and a horizontal underground heat exchanger for collecting heat by exchanging heat with the ground is buried below the foam resin board 3, thereby collecting ground heat with very high heat exchanging efficiency.